A resin transfer molding process begins with a fibrous pre-form that is inserted into a rigid mold die piece mold. In the mold, resin is injected at a low temperature into the pre-mold and cured. The curing process changes the resin into a pre-ceramic polymer material. The pre-ceramic polymer material is rigid and allows the part to be removed from the mold tool and pyrolized at very high temperatures. The pyrolized process at high temperature is conducted outside of the tool and converts the pre-ceramic polymer into a ceramic material. During the pyrolysis operation, a significant amount of polymer shrinkage occurs as it is converted into a ceramic material. The significant amount of shrinkage causes porosity including pores and cracks formed within the ceramic matrix.
After the first pyrolysis process, additional polymer infiltration processes are utilized to fill the pores and cracks that exist in the ceramic matrix from the first process. Additional cycles of the polymer infiltration and pyrolysis process are executed to increase the density and reduce the porosity within the part. However, each high temperature pyrolysis process causes distortion of the part and prevents the part from being reinserted into the original rigid tool utilized to inject resin into the pre-form. Accordingly, the current practice is to simply dip a part into resin, remove from the resin, and pyrolize outside of a rigid tool. However, such processes do not retain sufficient amount of liquid resin within the cores, voids and cracks of the ceramic part to adequately fill and provide the desired density of the completed part. Moreover, such a process often results in significant amounts of pre-ceramic polymer on outer surfaces of the ceramic part that must be machined or otherwise removed prior to the next pyrolysis operation.
Accordingly, it is desirable to develop a re-infiltration process to inject resin into a ceramic part to fill voids that minimizes the use of excess resin and provides for the more efficient infusion of resin into the cracks and voids formed within the part.